1. Field of the Invention
The present invention relates to an image forming apparatus capable of managing image formation status for each sheet.
2. Related Background Art
In the conventional image forming apparatus, there is only externally outputted the status information of the entire apparatus such as a state of preparing for printing, a state of image formation, a state of sheet carrying in progress, or the information on the number of sheet carried in the apparatus.
As the conventional image forming apparatus does not externally output the information on the individual sheet managed in the apparatus, it has been associated with following drawbacks, since the external device or the user utilizing such image forming apparatus is incapable of recognizing the state of carrying or printing of the individual sheet.
More specifically, in case the printing operation in the image forming apparatus is not completed in the normal state, the same image has to be printed after the image forming apparatus is restored to the normal state. As the completion of the image formation or of the sheet discharge on the individual sheet cannot be known from the outside, the external device sending the image information to the image forming apparatus has to retain the image formation with a certain marginal time after the output of the print instruction to the image formation apparatus, and such requirement limits the amount of the simultaneously storable image data.
Also in case the image forming apparatus is connected to a network, the operator is unable to recognize the state of execution of the printing job from the position of the operator, and, in case of an abnormality in the image forming apparatus, the operator has to go to the location of the image forming apparatus in order to confirm whether the printing job of the operator has been properly completed. Also, if the printing job has not been completed in proper state, the operator has to return to the location of the output device and to repeat the image output.
Also in case the image forming apparatus is connected to a sheet input/output device such as a large-capacity sheet feeding deck or a sheet sorter, the external control device for collectively controlling such input/output devices has to manage the sheet carrying state in the image forming apparatus by the timing based on a specified reference (for example the output of a print start command), and is therefore unable to exactly manage the transfer of the sheet among various devices. Particularly the sheet management becomes very difficult in case the order of printing in the image forming apparatus and the order of input/output of the sheets are mutually different, for example in case of two-side printing.
Also, some printing apparatus have a print reserving function for designating the print conditions in the order of execution. However, in the conventional printing apparatus with such print reserving function, the reserved printing job can be deleted only by the owner of the printing job, but there is not provided a function of deleting the job, changing the print condition or changing the order of reservations after the execution is started.
The printing operation by the printing apparatus is enabled after various units of the printing apparatus (printer engine) are activated in response to the print instruction from a host computer or the like. On the other hand, the print data forming apparatus (video controller) for supplying the printing apparatus with the print data forms the print data for supply to the printing apparatus based on the print information from an external device such as the host computer connected to the print data forming apparatus or from an operator. In general, in response to the reception of the print information from the exterior, the print data forming apparatus executes reservation of the printing operation in the printing apparatus, prior to the formation of the print data. Thus the starting-up of the printing apparatus to the printing state and the print data formation in the print data forming device are executed in parallel manner in order to shorten the time required to the start of the printing operation.
In case the print data forming apparatus receives plural print information from the exterior, plural print jobs may be reserved in the printing apparatus prior to the completion of the formation of the plural print data.
The printing apparatus having the print reserving function prepares for the execution of the printing in the order of the printing jobs reserved from the print data forming apparatus, and waits for the print instruction therefrom.
In the printing apparatus, the reserved printing job may become not executable during the print instruction stand-by state, namely in the period from the reservation of the printing job to the completion of the print data formation in the print data forming apparatus.
However, in the conventional printing apparatus not provided with the functions of changing the reserved print condition, changing the order of reservation or deleting the job after the start of execution, if plural print jobs are reserved and a print job with an earlier order of execution becomes not executable, all the print jobs of the subsequent order of execution become not executable.
Otherwise, in the conventional printing apparatus provided only with the function of collectively deleting the print reservations, in case a reserved print job becomes not executable, it is necessary to collectively delete all the print reservations and to execute the print reservations anew.
FIG. 36 is a block diagram of a control unit of a conventional printer.
There are shown a printer controller 1101 for executing communication with and image data reception from a host computer, development of received image data into the information printable by the printer, and signal exchange and serial communication with a printer engine control unit to be explained later; an engine control unit 1102 for controlling various units of the printer engine through signal exchange and serial communication with the printer controller; a sheet size detection unit 1103 for detecting the sheet size in the cassette and transmitting the information to the engine control unit; a sheet feed unit sheet presence/absence detection unit 1104 for detecting the presence/absence of the sheet in the cassette, manual sheet insertion slot, optional cassette and envelope feeder and transmitting the information to the engine control unit; an option presence/absence detection unit 1105 for confirming the state of connection of the options such as the optional cassette and the envelope feeder; a sheet carrying control unit 1106 for controlling the sheet carrying; an optical system control unit 1107 for controlling an optical system including for example a scanner motor and a laser; a fixing temperature control unit 1108 for controlling the temperature of a fixing unit and detecting the abnormality thereof; an option control unit 1109 for instructing the operation of the options such as the optional cassette and the envelope feeder; and a sensor input unit 1110 for detecting the presence/absence of the sheet in various carrying paths such as a registration path, a discharge path, a two-side path and an inversion path.
In the following there will be explained signals between the printer controller and the engine control unit. There are shown a /CPRDY signal 1111 indicating that the printer controller is in a state capable of communication with the engine; a /PPRDY 1112 indicating that the engine control unit is in a state capable communication with the printer controller; a /RDY signal 1113 indicating that the engine control unit is in a stand-by state capable of printing operation; a /PRNT signal 1114 for issuing a print demand from the printer controller to the engine control unit; a /TOP signal 1115 constituting a vertical synchronization signal outputted from the engine control unit to the printer controller; a /PRFD signal 1116 from the printer controller for causing the engine control unit to effect a sheet pre-feeding operation; a /BD signal 1117 constituting a horizontal synchronization signal outputted from the engine control unit to the printer controller; a /SCLK signal 1118 constituting a synchronization clock signal for serial communication; a /CMD signal 1119 constituting a command signal from the printer controller to the engine control unit; a /CBSY signal 1120 constituting a strobe signal for command output; a /STS signal 1121 indicating the status of the engine, to be outputted in response to a command from the printer controller; and a /SBSY signal 1122 for status output. FIG. 37 shows the timing of the serial communication mentioned above. In response to a command outputted from the printer controller, a corresponding status is outputted in 1-to-1 relationship. The synchronization clock signal is outputted from the printer controller. The serial communication is executed with 8 bits, in which the least significant bit LSB is used as a parity bit.
FIG. 38 shows a conventional printing sequence, which is independent from the exchange of command and status by the serial communication shown in FIG. 37.
Upon receiving the /PRNT signal from the printer controller 1101, the engine control unit 1102 executes a sheet feeding operation and a pre-rotation process for starting up the electrophotographic process. Then the /TOP signal is outputted to the printer controller 1101 for vertical synchronization for the image writing. Subsequently the printer controller 1101 sends the /PRFD signal to the engine control unit 1102, in order to start the feeding of a next sheet. In response, the engine control unit 1102 picks up a sheet. Then, in response to the /PRNT signal, the /TOP signal is outputted to execute the image writing. The above-explained sequence is repeated to execute the continuous printing operation.
In the above-described conventional printer, however, the engine control unit 1102 cannot execute the sheet feeding operation for the next page until the establishment of the vertical synchronization for the image data of the preceding page, namely until the reception of the /PRFD signal responding to the output of the /TOP signal. Consequently, the high-speed printing can only be achieved by selecting a sheet feeding speed higher than in the ordinary printing operation, thereby reducing the time required for sheet feeding.
Such high-speed sheet feeding is achieved for example by selecting the high or low sheet feeding speed with an exclusive motor in the sheet feeding system or providing a mechanism for switching the gear ratio, thus involving an increased cost. This drawback is particularly conspicuous in an image forming apparatus with a long sheet feeding path.